Anesthesia Student Survival Guide.pdf - Index of

Anesthetic techniques: reGionAl ● 195
tend to be hyperechoic. Color flow Doppler can be applied to distinguish blood
vessels from other structures.
Another advantage of ultrasound is the ability to view the nerve block needle
in its entirety as it approaches the target nerve, and then see the local anesthetic
spread around the nerve. As the cost, portability, and image resolution improve,
ultrasound will most likely become an integral part of regional anesthesia.
Case Study
A 58-year-old man is to undergo right total knee replacement (TKR). After a
thorough H&P and consultation, he elects to have the procedure under regional
anesthesia. He is otherwise healthy, though he smokes a pack of cigarettes a day
and does not exercise regularly due to his arthritic knee. He takes an NSAID
daily for pain and lately has been taking oxycodone and acetaminophen for
worsening pain.
Which dermatomes or nerves will you need to block to perform a total knee
replacement comfortably?
The anterior portion of the thigh and leg are innervated by the L3, L4, and
L5 dermatomes. The back of the knee, though not in the incision, is stimulated
nonetheless in TKR, and is innervated by S2. In addition, a thigh
tourniquet is usually employed to prevent blood loss, so L2 and possibly
L1 should be blocked. In practice, the femoral, lateral femoral cutaneous,
obturator, and portions of the sciatic nerve need to be blocked.
Which regional anesthetic techniques are suitable for total knee replacement?
Which will you choose?
In theory, several techniques are possible. Spinal anesthesia will reliably
block all the involved nerve roots, whether a plain solution or hyperbaric
solution containing glucose is used. Hyperbaric solutions produce higher
levels than are necessary, so plain solutions may be favored for the lower
incidence of hypotension. Epidural anesthesia is commonly used for TKR
and allows titration of local anesthetic to the desired level. Disadvantages
include a 5–10% incidence of failed or inadequate block (asymmetric anesthesia
or incomplete sacral nerve blockade). An additional advantage is the
ability to extend the block for either prolonged surgery or for postoperative